Enhanced directivity feed and feed array

ABSTRACT

Disclosed is a shaped horn in conjunction with a dielectric tube for enhanced aperture directivity that can achieve a near optimum efficiency. The shaped horn provides additional mode control to provide an improved off-axis cross-polarization response. The horn shape can be individually optimized for isolated horns or for horns in a feed array. The feed array environment can produce results that lead to a different optimized shape than the isolated horn. Lower off axis cross-polarization can result in improved efficiency and susceptibility to interference.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S.application Ser. No. 16/404,578 filed May 6, 2019, which is acontinuation application of U.S. application Ser. No. 15/806,181 filedNov. 7, 2017, which is a continuation of U.S. application Ser. No.14/633,427 filed Feb. 27, 2015, the content of each of which areincorporated herein by reference in their entireties for all purposes.

BACKGROUND

Satellite antennas using reflectors for gain and multiple feeds in theconfiguration of single-feed-per-beam (SFPB) or multiple-feeds-per-beam(MFPB) to produce contiguous spot beam patterns or area coveragepatterns have a limitation in which the feed aperture area can beinsufficient to illuminate the reflector efficiently. In general, thespillover energy may exceed the optimum value that can be achieved by asingle feed sized to provide a net optimum efficiency. In other words,the reflector aperture can be over illuminated and the energy radiatedby the feed spilling past the reflector boundary can be greater than theoptimum for net efficiency.

The over illumination condition can exist over the practical ranges offocal length values, and generally applies to single reflector opticsand to dual-reflector optics. The over illumination condition exists fortransmission type convergent optics (e.g., lens) as well as reflectorconvergent optics. Convergent optics captures radio frequency (RF)energy over a defined area and redirects the energy to a smaller area.The over illumination condition can occur for defocused or focusedpositions of feeds arranged in a contiguous manner to form contiguousspot beams with reasonable gain loss at the secondary pattern two-beamand three-beam cross-over locations. A similar over illuminationcondition may arise in the case of an MFPB configuration, where thereflector or lens feeds are defocused to configure a phased array fedreflector antenna.

An approach in SFPB spot beam satellite system applications to improvethe illumination uses multiple reflectors for a congruent coverage areaand assigns near focused feeds to reflectors in a manner to avoid havingcontiguous coverage beams within a single reflector.

Another solution uses feed clusters (e.g., 3, 7, 13 elements) andrelatively complex orthogonal waveguide beamforming networks to provideoverlapping excitation of adjacent feeds to form each beam.

Mitigation examples exist for the over-illumination condition, in whichthe modes within a feed horn are controlled in an attempt to produce anear uniform amplitude distribution at the horn aperture. In these modecontrol examples, the near uniform amplitude distribution can be anapproximation to the TEM mode in the feed horn structure. Anothermitigation example maximizes the feed aperture area in a triangular feedlattice and uses horns having a hexagonal shaped boundary. Neither ofthese configurations provides optimum illumination conditions and mayexhibit only marginal performance improvements over the more commongeometry limited configurations.

SUMMARY

In accordance with the present disclosure, an antenna may include areflector and an array of feeds. Each feed in the array may include ahorn having a multi-flare mode conversion section having several flareangles. Each feed may include a dielectric insert having a portion thatextends through a part of the multi-flare mode conversion section and aportion that extends beyond an aperture of the multi-flare modeconversion section.

The following detailed description and accompanying drawings provide abetter understanding of the nature and advantages of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

With respect to the discussion to follow and in particular to thedrawings, it is stressed that the particulars shown represent examplesfor purposes of illustrative discussion, and are presented in the causeof providing a description of principles and conceptual aspects of thepresent disclosure. In this regard, no attempt is made to showimplementation details beyond what is needed for a fundamentalunderstanding of the present disclosure. The discussion to follow, inconjunction with the drawings, make apparent to those of skill in theart how embodiments in accordance with the present disclosure may bepracticed. In the accompanying drawings:

FIG. 1 is a block diagram of a satellite communication system that canbe improved by various embodiments of the present disclosure.

FIG. 1A shows some details of a reflector antenna for satellite 105depicted in FIG. 1.

FIG. 2 is an isometric view of a feed assembly in accordance with anillustrative embodiment of the present disclosure.

FIG. 3 is an exploded view of the feed assembly illustrated in FIG. 2.

FIG. 3A is a cross-sectional view of the feed assembly illustrated inFIG. 2.

FIGS. 4 and 4A illustrate, respectively, an isometric view and a crosssectional view of an illustrative embodiment of a horn in accordancewith the present disclosure.

FIG. 5 shows another illustrative embodiment of a horn in accordancewith the present disclosure.

FIGS. 6A, 6B, 6C, and 6D illustrate various embodiments of a dielectricinsert in accordance with the present disclosure.

FIG. 7 shows a magnified portion of the cross-sectional view shown inFIG. 3A.

FIG. 8 is an isometric view of a feed assembly in accordance withanother embodiment of the present disclosure.

FIG. 8A is a hidden line view of the feed assembly illustrated in FIG.8.

FIGS. 9 and 9A illustrate, respectively, an isometric view and a hiddenline view of a diplexer-polarizer.

FIGS. 9B and 9C illustrate, respectively, an isometric view and a topview of another embodiment of a diplexer-polarizer.

FIG. 10 illustrates an example of a feed array in accordance with thepresent disclosure.

FIG. 11 illustrates a satellite reflector antenna configured with a feedarray in accordance with the present disclosure.

FIG. 12 illustrates an example of a design flow to design a feed inaccordance with the present disclosure.

FIG. 13 shows a computer system in accordance with some embodiments ofthe present disclosure.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of the present disclosure. It will be evident,however, to one skilled in the art that the present disclosure asexpressed in the claims may include some or all of the features in theseexamples, alone or in combination with other features described below,and may further include modifications and equivalents of the featuresand concepts described herein.

Satellite Communication Systems

FIG. 1 is a diagram of an example satellite communications system 100that may be improved by systems, methods, and devices of the presentdisclosure. Satellite communication system 100 includes a network 120interfaced with one or more gateway terminals 115. Gateway terminal 115may be configured to communicate with one or more user terminals 130 viasatellite 105. As used herein the term “communicate” may refer to bothtransmitting and receiving (i.e., bidirectional communication) or mayrefer to either transmitting or receiving (i.e., unidirectionalcommunication) over a particular pathway.

Gateway terminal 115 may be referred to herein as the hub or groundstation. Gateway terminal 115 may service uplink 135 and downlink 140 toand from satellite 105. Gateway terminal 115 may also schedule trafficto user terminals 130. Alternatively, the scheduling may be performed inother parts of satellite communication system 100. Although only onegateway terminal 115 is shown in FIG. 1 to avoid over complication ofthe drawing, embodiments in accordance with the present disclosure maybe implemented in satellite communication systems having multiplegateway terminals 115, each of which may be coupled to each other and/orone or more networks 120. Even in wideband satellite communicationsystems, the available frequency spectrum is limited. Communicationlinks between gateway terminal 115 and satellite 105 may use the same,overlapping, or different frequencies as communication links betweensatellite 105 and user terminals 130. Gateway terminal 115 may also belocated remotely from user terminals 130 to enable frequency reuse. Byseparating the gateway terminal 115 and user terminals 130, spot beamswith common frequency bands can be geographically separated to avoidinterference.

Network 120 may be any type of network and can include for example, theInternet, an IP network, an intranet, a wide area network (WAN), a localarea network (LAN), a virtual private network (VPN), a virtual LAN(VLAN), a fiber optic network, a cable network, a public switchedtelephone network (PSTN), a public switched data network (PSDN), apublic land mobile network, and/or any other type of network supportingcommunications between devices as described herein. Network 120 mayinclude both wired and wireless connections as well as optical links.Network 120 may connect gateway terminal 115 with other gatewayterminals that may be in communication with satellite 105 or with othersatellites.

Gateway terminal 115 may be provided as an interface between network 120and satellite 105. Gateway terminal 115 may be configured to receivedata and information directed to one or more user terminals 130. Gatewayterminal 115 may format the data and information for delivery torespective terminals 130. Similarly gateway terminal 115 may beconfigured to receive signals from satellite 105 (e.g., from one or moreuser terminals 130) directed to a destination accessible via network120. In some embodiments, gateway terminal 115 may also format thereceived signals for transmission on network 120. In some embodiments,gateway terminal 115 may use antenna 110 to transmit forward uplinksignal 135 to satellite 105. Antenna 110 may comprise a reflector withhigh directivity in the direction of satellite 105 and low directivityin other directions. Antenna 110 may comprise a variety of alternativeconfigurations which include operating characteristics such as highisolation between orthogonal polarizations, high-efficiency in theoperational frequency band, low noise, and the like.

Satellite 105 may be a geostationary satellite that is configured toreceive forward uplink signals 135 from the location of antenna 110using a reflector antenna (not shown) described in more detail belowwith respect to FIG. 1A. Satellite 105 may receive the signals 135 fromgateway terminal 115 and forward corresponding downlink signals 150 toone or more of user terminals 130. The signals may be passed through atransmit reflector antenna (e.g., reflector antenna described in moredetail below with respect to FIG. 1A) to form the transmission radiationpattern (e.g., a spot beam). Satellite 105 may operate in multiple spotbeam mode, transmitting and receiving a number of narrow beams directedto different regions on the earth. This allows for segregation of userterminals 130 into various narrow beams. Alternatively, the satellite105 may operate in wide area coverage beam mode, transmitting one ormore wide area coverage beams to multiple receiving user terminals 130simultaneously.

Satellite 105 may be configured as a “bent pipe” or relay satellite. Inthis configuration, satellite 105 may perform frequency and polarizationconversion of the received carrier signals before retransmission of thesignals to their destination. A spot beam may use a single carrier, i.e.one frequency, or a contiguous frequency range per beam. In variousembodiments, the spot or area coverage beams may use wideband frequencyspectra. A variety of physical layer transmission modulation encodingtechniques may be used by satellite 105 (e.g., adaptive coding andmodulation). Satellite 105 may use on-board beamforming techniques orrely on off-board (ground based) beamforming techniques.

Referring for a moment to FIG. 1A, in some embodiments, a reflectorantenna 106 for satellite 105 may comprise a reflector 112 and a feedassembly 114 (described in more detail below) to illuminate thereflector 112 in accordance with the present disclosure. The figureshows an offset parabolic reflector configuration. However, embodimentsin accordance with the present disclosure may use other antennaconfigurations. In some embodiments, the reflector 112 may be parabolicas depicted in FIG. 1A, for example. In other embodiments, the reflector112 may have any spherical, aspherical, bi-focal, or offset concaveshaped profile necessary for the generation of the desired transmissionand receiving beams. In other embodiments, the reflector 112 may be usedin conjunction with one or more additional reflectors in a system ofreflectors. The system of reflectors may be comprised of one or moreprofiles such as parabolic, spherical, ellipsoidal, or shaped, and maybe arranged in classical microwave optical arrangements such asCassegrain, Gregorian, Dragonian, offset, side-fed, front-fed orsimilarly configured optics systems known in the art.

Returning to FIG. 1, satellite communication system 100 may use a numberof network architectures consisting of space and ground segments. Thespace segment may include one or more satellites 105 while the groundsegment may include one or more user terminals 130, gateway terminals115, network operation centers (NOCs) and satellite and gateway terminalcommand centers. The terminals may be connected by a mesh network, astar network, or the like as would be evident to those skilled in theart.

Forward downlink signals 150 may be transmitted from satellite 105 toone or more user terminals 130. User terminals 130 may receive downlinksignals 150 using antennas 127. In one embodiment, for example, antenna127 and user terminal 130 together comprise a very small apertureterminal (VSAT), with antenna 127 measuring approximately 0.6 m indiameter and having approximately 2 W of power. In other embodiments, avariety of other types of antenna 127, including PAFR antennas, may beused as user terminals 130 to receive downlink signals 150 fromsatellite 105. Each of the user terminals 130 may comprise a single userterminal or, alternatively, may comprise a hub or router, not shown,that is coupled to multiple user terminals. Each user terminal 130 maybe connected to various consumer electronics comprising, for example,computers, local area networks, Internet appliances, wireless networks,and the like.

In some embodiments, a multi-frequency time division multiple access(MF-TDMA) scheme may be used for upstream links 140 and 145, allowingefficient streaming of traffic while maintaining flexibility andallocating capacity among each of the user terminals 130. In theseembodiments, a number frequency channels may be allocated statically ordynamically. A time division multiple access (TDMA) scheme may also beemployed in each frequency channel. In this scheme, each frequencychannel may be divided into several timeslots that can be assigned to aconnection (i.e., a user terminal 130). In other embodiments, one ormore of the upstream links 140, 145 may be configured using otherschemes, such as frequency division multiple access (FDMA), orthogonalfrequency division multiple access (OFDMA), code division multipleaccess (CDMA), or any number of hybrid or other schemes known in theart.

User terminal 130 may transmit data and information to a network 120destination via satellite 105. User terminal 130 may transmit thesignals by upstream link 145 to satellite 105 using antenna 127. Userterminal 130 may transmit the signals according to various physicallayer transmission modulation encoding techniques, including forexample, those defined with the DVB-S2, WiMAX, LTE, and DOCSISstandards. In various embodiments, the physical layer techniques may bethe same for each of the links 135, 140, 145, 150, or they may bedifferent.

Satellite 105 may support non-processed, bent pipe architectures withone or more reflector antennas as described herein to produce multiplesmall spot beam patterns. The satellite 105 can include J genericpathways, each of which can be allocated as a forward pathway or areturn pathway at any instant of time. Large reflectors may beilluminated by a phased array of feeds to provide the ability to makearbitrary spot and area coverage beam patterns within the constraintsset by the size of the reflector and the number and placement of thefeeds. Reflector antennas may be employed for both receiving uplinksignals 130, 140, transmitting downlink signals 140, 150, or both in afull duplex mode. The beam forming networks (BFN) associated with thereceive (Rx) and transmit (Tx) reflector antennas may be dynamic,allowing for quick movement of the locations of both the Tx and Rxbeams. The dynamic BFN may be used to quickly hop both Tx and Rxwideband beam positions.

Feed Assembly

FIG. 2 shows an illustrative embodiment of feed assembly 114 (FIG. 1A)in accordance with the present disclosure. In some embodiments, the feedassembly 114 may comprise a feed 202. The feed 202 may comprise a horn204 and a dielectric insert 206. The dielectric insert 206 may have afirst portion (e.g., 362, FIG. 3) disposed within the horn 204, and asecond portion (e.g., 362, FIG. 3) that extends beyond an aperture 242of the horn 204.

In some embodiments, the feed assembly 114 may further comprise awaveguide 212 to guide the electromagnetic (EM) waves of a transmitsignal or a received signal between a coupling flange 216 and the feed202. For example, the waveguide 212 may provide a transmit signal,produced by transceiver 20 (or other suitable transmitter unit) andreceived at an input port (e.g., 316 a, FIG. 3A) of the coupling flange216, to feed 202 for transmission by an antenna (e.g., reflector antenna106, FIG. 1A). Conversely, the waveguide 212 may provide a signalreceived by the antenna (e.g., reflector antenna 106, FIG. 1A) to anoutput port (e.g., 316 b, FIG. 3A) of the coupling flange 216 to thetransceiver 20 (or other suitable receiver unit). In some embodiments,the waveguide 212 may be a rectangular waveguide (e.g., a squarewaveguide). In other embodiments, the waveguide 212 may be a circularwaveguide. In some embodiments, the waveguide 212 may be ridge loaded,and in other embodiments other waveguide configurations may be used.

In some embodiments, the feed assembly 114 may further comprise anadapter 214 coupled to the waveguide 212. The adapter 214 may be afilter, a polarizer, a diplexer, or other suitable radio frequency (RF)component. In various embodiments, for example, the adapter 214 may be afour-port or two-port orthomode transducer (OMT), the adapter 214 may bea single-band or dual-band septum polarizer, and so on. In otherembodiments, the adapter 214 may be a combination of a polarizer and adiplexer, the adapter 214 may be a combination of a polarizer and afilter (e.g., high pass, low pass, bandpass), and so on.

The coupling flange 216 may be used to mount the feed assembly 114 to asuitable structural support and/or to other antenna structures. Asexplained above, the coupling flange 216 may include ports (e.g., 316 a,316 b, FIG. 3A) that serve as an input port and an output port.

FIG. 3 shows an exploded view of the feed assembly 114 depicted in FIG.2. In accordance with some embodiments, the horn 204 may be circularwaveguide comprising a first waveguide section 342 and a secondwaveguide section 344 coupled to or otherwise joined to the firstwaveguide section 342. The first waveguide section 342 may be a circularwaveguide. The second waveguide section 344 may be referred to herein asa multi-flare mode conversion section 344. The multi-flare modeconversion section 344 may be characterized by several different flareangles between a first end 352 and a second end 354 of the multi-flaremode conversion section 344.

The dielectric insert 206 may comprise a first portion 362, which can bedisposed within the volume of the horn 204. A second portion 364 of thedielectric insert 206 may extend beyond the aperture 242 of horn 204.

The waveguide 212 may include a collar 302 configured to couple thewaveguide 212 the horn 204, for example, at the first waveguide section342. Locking screws 304 may secure the horn 204 and/or dielectric insert206 to the waveguide 212. The locking screws 304 may, for example, bemade from electrically conductive material such as metal. As anotherexample, the locking screws 304 may be made from non-conductivematerial. In some embodiments, the horn 204 may be fixedly attached tothe first waveguide section 342 using a welding or bonding technique. Insome embodiments, the horn 204 and first waveguide section 342 may bemade of a single additive construction method such as electroforming ordirect laser sintering or other known manufacturing processes in theart. In some embodiments, a waveguide seal 306 may be provided to blockor otherwise reduce RF leakage where the horn 202 joins the waveguide212. In some embodiments, a secondary dielectric insert (not shown) maybe installed surrounding the dielectric insert 206 to secure thedielectric insert 206 to the waveguide 212.

FIG. 3A shows a cross sectional view of the feed assembly 114 depictedin FIG. 2. The cross sectional view illustrates that, in someembodiments, the first portion 362 of dielectric insert 206 may extendthrough the multi-flare mode conversion section 344 of horn 204. Thesecond portion 364 may extend beyond the aperture 242 of horn 204 by agiven length, L. The cross sectional view further illustrates the inputport and the output port formed through the coupling flange 216.

FIG. 4 shows details of horn 204 in accordance with the presentdisclosure. In some embodiments, the horn 204 may comprise several hornsegments 412 a, 412 b, 412 c, 412 d. For example, the first waveguidesection 342 may comprise horn segment 412 a. The multi-flared modeconversion section 344 may comprise horn segments 412 b, 412 c, 412 d.It will be appreciated that either or both the first waveguide section342 and the multi-flared mode conversion section 344 may comprise feweror more horn segments.

The horn segments 412 a-412 d may have a circular cross section. In someembodiments, the horn segments 412 a-412 d may be a metal such ascopper, aluminum, etc. In other embodiments, the horn segments 412 a-412d may be a metal alloy such as brass, zinc alloy, etc. Each horn segment412 a, 412 b, 412 c may be joined to a respective horn segment 412 b,412 c, 412 d, defining respective transitions 414 a, 414 b, 414 c at thejoints. Any suitable joining technique may be used to join the hornsegments 412 a-412 d, including, for example, soldering, brazing,welding, and the like.

In accordance with the present disclosure, a cross sectional diameter dof the horn 204 may vary along the axial length of the horn 204, thusshaping the horn 204. Referring to FIG. 4A, a cross-sectional view ofthe horn 402 illustrates that, in some embodiments, horn segments 412 a,412 b, 412 c, 412 d can shape the horn 204 in piece-wise fashion using alinear series of flare angle changes to vary the diameter d. The hornsegments 412 a, 412 b, 412 c, 412 d may be conical frusta withrespective constant flare angles (e.g., the diameter d may vary linearlyin a given horn segment), or cylinders (e.g., the diameter d may remainconstant in a given horn segment). For example, in the particularembodiment shown in FIG. 4A, horn segments 412 b and 412 d are conicalfrusta configured to define respective flare angles θ₂ and θ₃ measuredrelative to an axis of the horn 204. In the particular embodiment shown,horn segment 412 c is a cylinder, having no flare (e.g., the flare angleis 0°, diameter d is constant). In the particular embodiment of FIG. 4A,horn segment 412 a includes a portion that is a cylinder and a portionthat is a conical frustum.

In the particular embodiment illustrated in FIG. 4A, the horn segments412 a, 412 b, 412 d have respective flare angles θ₁, θ₂, θ₃, and hornsegment 412 c has a 0° flare angle. When the horn segments 412 a, 412 b,412 c, 412 d are joined, the flare angle along the axial length of horn204 varies from θ₁ to θ₂ to 0° and then to θ₃, respectively, at atransition within horn segment 412 a and at transitions 414 a, 414 b,414 c. In some embodiments, the flare angles may be different from oneanother. In other embodiments, some of the flare angles may be the same.

In some embodiments, the transitions of flare angles along the axiallength of the horn 204 may be smooth or gradual. For example, thetransitions 414 a, 414 b, 414 c illustrated in FIG. 4A are discrete andhave sharp corners. In other embodiments, the transitions 414 a, 414 b,414 c may be rounded or smoothed out; e.g., by buffing the corners.

Whereas each horn segment 412 b, 412 c, 412 d in FIG. 4A is defined by acorresponding constant flare angle, in other embodiments, the flareangle may change continuously along the axial length of the horn toprovide a smooth walled horn. FIG. 5, for example, shows a horn 504comprising a multi-flare mode conversion section 544 having flare anglesthat vary in a continuous manner along an axial length of the horn 504.Thus, for example, the flare angle may be represented by a line tangentto each point (e.g., p1, p2, p3) on a cross sectional profile of horn504 whose angle relative to the axis of the horn 504 varies from onepoint to the next. Stated differently, the cross sectional diameter d ofhorn 504 may vary continuously along its axial length. In someembodiments, for example, the change in diameter d may be defined by oneor more continuous functions. For example, a spline may be used todefine the cross sectional profile of horn 504 to define a flare anglethat continuously varies along the axial length of the horn 504.

In some embodiments, the multi-flare mode conversion section may be asingle-piece construction. The horn 504 in FIG. 5, for example,comprises a single-piece multi-flare mode conversion section 544. Thehorn 504 may further comprise a sleeve 542 joined to the multi-flaremode conversion section 544. The sleeve 542 may be configured to couplethe horn 504 to a waveguide (e.g., 212, FIG. 2).

FIG. 6A shows additional details of dielectric insert 206 in accordancewith the present disclosure. In some embodiments, the dielectric insert206 may be a tube, a rod, or other suitable elongate structure. Theparticular structure selected may be decided based on factors such asmechanical stability, thermal stability, expected operating environment,and so on. As noted above, the first portion 362 of dielectric insert206 may be configured for being positioned and supported within the horn204. In some embodiments, the first portion 362 may include fingers 602configured to secure the dielectric insert 206 to the horn 204. FIGS. 6Band 6C show alternate configurations of the fingers 602. Referring for amoment to FIG. 7, a magnified portion of the cross sectional view shownin FIG. 3A illustrates that dielectric insert 206 may be disposed withinthe throat of the horn 204. The fingers 602 of the dielectric insert 206can provide a friction fit with the interior surface of horn 204 for aself-supporting structure. The locking screws 304 may help to secure thedielectric insert 206 in position. In other embodiments, a web-likestructure (not shown) may be used to support the dielectric insert 206.

In some embodiments, the dielectric insert 206 may be a dielectricmaterial comprising a quartz fiber weave construction supported by acyanate-ester resin system that exhibits low-loss RF performance andsuitable mechanical properties for the environment. In otherembodiments, plastic materials such as Rexolite® plastic or Ultem®plastic may be used. In general, the dielectric insert 206 may compriseany material or combination of materials having suitable dielectricproperties, mechanical properties, thermal properties and the like.

FIG. 6D shows a cross-sectional view of an alternative embodiment of thedielectric insert 206. In this embodiment, the dielectric insert 206 isa dielectric tube having an inner diameter 650 and an outer diameter652. As can be seen in the figure, in the illustrated embodiment boththe diameters 650, 652 decrease with distance from the location 656where the dielectric insert 206 contacts the interior surface of horn204. In other embodiments, only one of the diameters 650, 652 maydecrease with distance from the location 626. Decreasing the distance ofone or both of the diameters 650, 652 may provide improved performanceover a wide frequency range, such as the low frequency band and the highfrequency band of a diplexer-polarizer unit (discussed below) of thefeed assembly. In some embodiments, the thickness 654 of the dielectrictube may be constant with distance from the location 652. In otherembodiments, the thickness 654 may vary with distance from the location652. For example, the thickness 654 may decrease with distance from thelocation 652, such as linearly decreasing with distance. Decreasing thethickness 654 may also provide improved performance over a widefrequency range, such as the low frequency band the high frequency bandof the diplexer-polarizer unit (discussed below).

Operational characteristics of a feed (e.g., 202, FIG. 2) in accordancewith the present disclosure will now be discussed. The term “dominantwaveguide mode” refers to the propagation mode in a waveguide thatpropagates with minimum degradation (e.g., propagates with the lowestcutoff frequency). Furthermore, one of ordinary skill understands thatthe propagation modes in a waveguide may include:

-   -   transverse electromagnetic (TEM) mode—This is a propagation mode        in which neither the electric field nor the magnetic field are        in the direction of propagation.    -   transverse electric (TE) mode: This is a propagation mode in        which there is no electric field in the direction of        propagation, but there is a non-zero magnetic field along the        direction of propagation.    -   transverse magnetic (TM) mode: This is a propagation mode in        which there is no magnetic field in the direction of        propagation, but there is a non-zero electric field along the        direction of propagation.    -   hybrid mode: This is a propagation mode in which there is a        non-zero electric field and a non-zero magnetic field along the        direction of propagation.

As explained with reference to FIGS. 2-4, the feed 202 comprises a horn204 and a dielectric insert 206. The multi-flare mode conversion section344 of horn 204 may function in conjunction with the first portion 362of dielectric insert 206 to convert a signal between a dominantwaveguide mode and a hybrid mode. The hybrid mode may propagate alongthe second portion 364 of the dielectric insert 206 to define anillumination beam toward a reflector (e.g., 112, FIG. 1A).

In some embodiments, the feed 202 may be used to transmit a transmitsignal. Waveguide 212 can propagate the transmit signal in its dominantwaveguide mode. The transmit signal may, for example, be provided to thewaveguide 212 from a signal source (e.g., transceiver 20) via one ormore suitable RF components such as those discussed above. Themulti-flare conversion section 344 of the horn 204 may function inconjunction with the first portion 362 of the dielectric insert 206 toconvert the transmit signal from the dominant waveguide mode to thehybrid mode. The hybrid mode may then propagate along the second portion364 of the dielectric insert 206 and radiate largely from the distal endof the dielectric insert 206 to define the illumination beam directedtoward the reflector. The reflector can then reflect the illuminationbeam to form a desired secondary beam in which the reflectedelectromagnetic energy adds constructively in a desired direction (e.g.the direction corresponding to the satellite), while partially orcompletely cancelling out in all other directions.

In other embodiments, the feed 202 may be used to receive a receivesignal. The reflector can cause electromagnetic energy of the receivedsignal to converge at the location of the feed 202 if an incident planewave arrives from a desired direction (e.g., the direction correspondingto the satellite). The second portion 364 of the dielectric insert 206can cause the converged electromagnetic energy to propagate along it inthe hybrid mode. The multi-flare conversion section 344 of the horn 204may function in conjunction with the first portion 362 of the dielectricinsert 206 to convert the receive signal from the hybrid mode to thedominant waveguide mode. Waveguide 212 can then propagate the transmitsignal in its dominant waveguide mode and provide the transmit signal toa receiver (e.g., transceiver 20) via one or more suitable RF componentssuch as those discussed above.

In other embodiments, the feed 202 may be used to both transmit atransmit signal and receive a receive signal. The operation may, forexample, be full duplex, may be time duplexed, or may be a combinationof time duplexed with different and varying intervals of transmit andreceive signal flow.

The radiation pattern from the hybrid mode has the often desirableproperties of circular symmetry or pseudo circular symmetry in the mainbeam to a significant degree and corresponding low off axiscross-polarization energy. The hybrid mode radiation pattern is furtherdefined as having high purity Huygens polarized source properties. Insome embodiments, the dominant waveguide mode is a TE mode, which istypical in square waveguides and circular waveguides.

In accordance with the present disclosure, the hybrid mode produced byfeed 202 may have minimal or at least reduced cross-polarization energy.Cross polarization refers to the polarization orthogonal to thepolarization being discussed. For instance, if the fields from anantenna are meant to be horizontally polarized, the cross-polarizationin this case would be vertical polarization. As another example, if thepolarization is right hand circularly polarized, the cross-polarizationwould be left hand circularly polarized. The cross polarization energymay be expressed as a power level in units of dB, indicating how manydecibels below the desired polarization's power level the crosspolarization power level is, and is known as cross-polarizationdiscrimination (XPD). In some embodiments, the XPD of the illuminationbeam may be less than −24.5 dB.

In some embodiments, the signal may comprise several frequencies(frequency components). The multi-flare mode conversion section 344 ofhorn 204 may function in conjunction with the first portion 362 ofdielectric insert 206 to convert the signal between a dominant waveguidemode and a hybrid mode at each frequency. In some embodiments, the ratiobetween the frequency of the highest frequency component in the signaland the frequency of the lowest frequency component in the signal may beabout 1.5 or higher. In some embodiments, the axial ratio of theillumination beam may be less than 1 dB at each of the frequencies whenexpressed as the ratio of the large quantity over the small quantity.

In accordance with the present disclosure, the dielectric insert 206 canimprove the directivity of the illumination beam. In some embodiments,directivity may be computed as a ratio of the power of the signalmeasured along the axis of propagation to the total power in the signal.Propagation of the hybrid mode may be largely confined to the secondportion 364 of the dielectric insert 206 to improve directivity. Forexample, in a configuration comprising only a horn and no dielectricinsert, the illumination beam propagates along the horn and radiatesfrom the aperture of the horn. The directivity of this illumination beammay be less than the directivity of an illumination beam that propagatesalong a dielectric insert (e.g., 206) and radiates from the distal endof the dielectric insert. The improved directivity may be useful in afeed array (e.g., 1000, FIG. 10) because increased directivity canmitigate the challenge of having to isolate the individual horns in thefeed array.

Increasing the length L of the second portion 364 of the dielectricinsert 206 may increase feed directivity. However, the distribution ofenergy in the illumination beam decreases as the length L increases.Therefore, in a particular implementation, design decisions might bemade to trade off energy distribution in the illumination beam fordirectivity of the secondary beam of the reflector. The reflector edgeillumination values can be an indication of optimum illumination and thetrade off between the portion of energy illuminating the reflector andthe portion of energy spilling past the reflector (spillover energy). Anedge illumination of approximately −8 to −14 dB relative to a centralpeak value can result in near optimum net efficiency and can be achievedwith a feed assembly in accordance with the present disclosure. In someembodiments, the edge illumination may be less than −14 dB (e.g., −18dB). In an example, a dual band full duplex feed may be designed for anear optimum illumination in a lower frequency band, and underilluminate the reflector in a higher frequency band. A single transmitor receive reflector with a SFPB horn design in either a focused ornon-focused configuration with dense contiguous feeds in an arraywithout the dielectric insert may have an edge illumination value ofapproximately −5 dB relative to a central peak value and will besubstantially below the optimum illumination as a result of thespillover energy. The portion of cross-polarization energy detracts fromthe overall performance of the antenna system when frequency reuse andpolarization are applied to provide isolated areas of coverage in theform of spot beams. Minimizing the cross-polarization is an oftenapplied design objective in systems that use polarization for coveragesignal isolation.

A feed assembly (e.g., 114, FIG. 2) in accordance with the presentdisclosure may be used with any suitable RF component. FIG. 8, forexample, shows an illustrative embodiment of a feed assembly 814 inaccordance with the present disclosure. The feed 802 may comprise a horn804 and a dielectric insert 806. The horn 804 may comprise asingle-piece multi-flare mode conversion section 844 coupled to a sleeve842. The dielectric insert 806 may have a first portion (not shown)disposed within the horn 804, and a second portion that extends beyondan aperture 842 of the horn 804.

In some embodiments, the feed assembly 814 may further comprise ahousing 824 which may house an RF component (not shown). In someembodiments, the RF component may be a diplexer-polarizer unit (826,FIG. 8A). It will be appreciated, of course, that in other embodiments,the feed 802 may be used with RF components other than adiplexer-polarizer. For example, in some embodiments, the feed 802 maybe used in combination with RF components such as a four-port OMT, atwo-port OMT, a single-band septum polarizer, a dual-band septumpolarizer, a polarizer and a filter, and so on.

Referring to FIG. 8A, the hidden line view of feed assembly 814 shown inthe figure illustrates that a portion of the dielectric insert 806 mayextend into the horn 804 and through the multi-flare mode conversionsection 844 where the dielectric insert 806 can be supported at thethroat of horn 804. A portion of the dielectric insert 806 may extendbeyond the aperture 842 of horn 804. The figure shows thediplexer-polarizer unit 826 disposed within the housing 824.

FIG. 9 shows an illustrative embodiment of diplexer-polarizer unit 826depicted in FIG. 8A. The diplexer-polarizer unit 826 may comprise adiplexer 902, waveguides 904 a, 904 b coupled to the diplexer 902, and apolarizer 906. In some embodiments, the diplexer 902 may be a 4-portdiplexer. The waveguides may be divided into high-side waveguides 904 ato transmit and receive signals in a high frequency band and low-sidewaveguides 904 b to transmit and receive signals in a low frequencyband, as indicated by dividing plane 92. Merely to provide anillustrative example of the use of a diplexer-polarizer for a dual-bandfull-duplex configuration, the high frequency band may span a range ofabout 27.5-31.0 GHz (a bandwidth of about 3.5 GHz) and the low frequencyband may span a range of about 17.7-21.2 GHz (a bandwidth of about 3.5GHz).

The waveguides 904 a, 904 b may be further divided according to thepolarization of the signal propagated in the waveguides, as indicated bydividing plane 94. For example, the high-side waveguides 904 a maycomprise one waveguide configured to transmit and receive right handcircularly polarized signals and another waveguide configured totransmit and receive left hand circularly polarized signals. Similarly,the low-side waveguides 904 b may comprise one waveguide to transmit andreceive right hand circularly polarized signals and another waveguide totransmit and receive left hand circularly polarized signals.

FIG. 9A is a hidden line representation of the diplexer-polarizer unit826. In some embodiments, the polarizer 906 may comprise a squarewaveguide 962 having a staircase septum polarizer 964 disposed withinthe square waveguide 962. The septum polarizer 964 may divide thewaveguide 962 into a first waveguide portion 966 a and a secondwaveguide portion 966 b, as indicated in the figure by the dividingplane 96. The septum polarizer 964 may be configured to convert signalsbetween a polarized state in the waveguide 962 and a first polarizationcomponent in the first waveguide portion 966 a and a second polarizationcomponent in the second waveguide portion 966 b. In some embodiments,the first polarization component may correspond to a first polarizationat the aperture 842 of horn 802 shown in FIG. 8. Similarly, the secondpolarization component may correspond to a second polarization at theaperture 842 of horn 802. In some embodiments, the first polarizationmay be a first circular polarization and the second polarization may bea second circular polarization different from the first circularpolarization.

The hidden line representation of FIG. 9A reveals that waveguides 904 acomprise high-side ports 942 a, 942 b and waveguides 904 b compriselow-side ports 944 a, 944 b. In some embodiments, the ports 942 a and944 a may be configured to transmit and receive right hand circularlypolarized signals, and the ports 942 b, 944 b may be configured totransmit and received left hand circularly polarized signals.

FIG. 9B shows a perspective view of an air model of an alternativeembodiment of diplexer-polarization unit 826. FIG. 9C is a top view ofthe diplexer-polarization unit 826 of FIG. 9B. In the illustration ofFIG. 9B, the diplexer-polarization unit 826 is rotated 90-degrees alongthe axis of the polarizer 906 relative to the illustration in FIGS. 9and 9A. The septum polarizer 964 may divide the waveguide 962 into firstwaveguide portion 966 a and second waveguide portion 966 b. As indicatedby dividing plane 98, the first waveguide portion 966 a is associatedwith a first polarization and the second waveguide portion 966 b isassociated with a second polarization. In the illustrated example, thefirst polarization is left hand circularly polarized, and the secondpolarization is right hand circularly polarized. Alternatively, thepolarizations may be different.

Diplexer 902 incudes a first pair of waveguides 932 coupled to the firstwaveguide portion 966 a. The first pair of waveguides 932 includes ahigh-side waveguide 932 a and a low-side waveguide 932 b. The high-sidewaveguide 932 a includes a filter configured to communicate signals inthe high frequency band between the first waveguide portion 966 a andhigh-side port 952 a. Similarly, the low-side waveguide 932 b includes afilter configured to communicate signals in the low frequency bandbetween the first waveguide portion 966 a and low-side port 954 a. Inthe illustrated example, each of the filters of the high-side andlow-side waveguides 932 a, 932 b include multiple E-plane elements thatmay be of varying stub lengths with varying lengths of interconnectingwaveguides between the E-plane elements. In other embodiments, eachfilter may be different. In some embodiments, each filter may include atleast one of an input matching section and an output matching section.

Diplexer 902 further includes a second pair of waveguides 934 coupled tothe second waveguide portion 966 b. The second pair of waveguides 934includes a high-side waveguide 934 a and a low-side waveguide 934 b. Thehigh-side waveguide 934 a includes a filter configured to communicatesignals in the high frequency band between the second waveguide portion966 b and high-side port 952 b. Similarly, the low-side waveguide 934 bincludes a filter configured to communicate signals in the low frequencyband between the second waveguide portion 966 b and low-side port 954 b.In the illustrated example, the filters of the high-side and low-sidewaveguides 934 a, 934 b are the same as those of the high-side andlow-side waveguides 932 a, 932 b respectively. In other embodiments, thefilters may be different. In some embodiments, each filter may includeat least one of an input matching section and an output matchingsection.

In the illustrated embodiment of FIGS. 9B and 9C, the 4 ports 952 a, 952b, 954 a, 954 a of the diplexer 902 are arranged in a row along anE-plane of the pairs of waveguides 932, 934 in a direction normal to thedividing plane 98. Having the ports arranged in a row can permitefficient transition to an edge-launch circuit board interface within atransceiver (e.g., ref. no. 20 of FIG. 2) In the illustrated example,the low-side ports 954 a, 954 b are arranged between the high-side ports952, 952 b. Accordingly, in this example the filter of low-sidewaveguide 932 b has a first waveguide wall that is shared with thefilter of high-side waveguide 932 a, and has a second waveguide wallthat is shared with the filter of low-side waveguide 934 b. Similarly,the low-side waveguide 934 b has a first (already mentioned) waveguidewall that is shared with the filter of the low-side waveguide 932 b, anda second waveguide wall that is shared with the filter of the high-sidewaveguide 934 a. As used herein, shared waveguide walls refers toconductive material (e.g., metal) having a first surface that forms thewaveguide wall of a first filter of a first waveguide and having asecond surface opposing the first surface that forms the waveguide wallof a second filter of a second waveguide, where the conductive materialextends between the first surface and the second surface. The conductivematerial extending between the first surface and the second surface mayfor example be a solid material or a web of interconnected material.Having the filters share walls can provide one or more benefitsincluding minimizing the amount of material needed to form the diplexer902, minimizing the mass of the diplexer 902, and/or maximizing thevolumetric efficiency of the diplexer. In other embodiments, the pairsof waveguides may be arranged differently (e.g., in a 2×2 arrangement asshown FIGS. 9 and 9A), and thus the filters that share walls can bedifferent.

Referring to FIG. 10, in some embodiments, a feed array 1000 maycomprise an array of feed assemblies 1002 in accordance with the presentdisclosure. Illustrative examples of feed assemblies 1002 are shown inFIGS. 2 and 8. In some embodiments, the spacing (e.g., center-to-centerspacing, s) between the horns of adjacent feed assemblies 1002 may bethe same. Merely to illustrate, for example, in some embodiments, thespacing s between the horns of adjacent feed assemblies 1002 may beabout 2.5 wavelengths of a highest frequency of the signal to betransmitted or received. In other embodiments, the spacing S betweenhorns of adjacent feed assemblies 1002 may vary.

The feed assemblies 1002 comprising the feed array 1000 may be arrangedin a regular pattern. In some embodiments, for example, the feedassemblies 1002 may be arranged in a lattice. For example, feedassemblies 1002 shown in FIG. 10 are arranged in a hexagonal lattice. Insome embodiments, the feed assemblies 1002 may be arranged in arectilinear pattern. In other embodiments, the feed assemblies 1002 maybe arranged in a triangular pattern. In still other embodiments, thefeed assemblies 1002 may be arranged in an irregular pattern.

In some embodiments, the feed assemblies 1002 comprising the feed array1000 may be arranged in a planar configuration. For example, the feedassemblies 1002 may be disposed on a planar surface so that the distalends of the dielectric inserts of the feed assemblies 1002 lie on aplane. In other embodiments, the feed assemblies 1002 comprising thefeed array 1000 may be arranged in non-planar configurations. Forexample, in some embodiments, the feed array 1000 may be arranged on aconvex surface or a concave surface relative to the curvature of thereflector (e.g., 112, FIG. 1A). More generally, in other embodiments,the feed array 1000 may be arranged on a surface having any suitablecontour.

The feed array 1000 may be incorporated in a reflector antenna of asatellite. FIG. 11, for example, shows a reflector antenna 1100 for asatellite (e.g., satellite 105, FIG. 1) that incorporates feed array1000. The reflector antenna 1100 is an example of an offset fedparabolic reflector configuration. However, it will be appreciated thatthe feed array 1000 may be incorporated in other antenna configurations.

In the configuration shown in FIG. 11, the feed array 1000 lies withinthe focal plane of the reflector 1112. In other embodiments, the feedarray 1000 may lie on the focal plane, or beyond the focal plane ofreflector 1112.

Referring to FIG. 12, a process for designing a feed (e.g., 202, FIG. 2)in accordance with the present disclosure will be explained. In someembodiments, the process may be performed using suitable simulationtools. The feed may be designed using, for example, the High FrequencyStructure Simulator (HFSS) software available from Ansys, Inc.Alternatively, other software may be used to design the feed.

At block 1202, a suitable reflector (e.g., 112, FIG. 1A) design may beselected. For example, the shape of the reflector may be specified, thedimensions of the reflector may be specified, and so on.

At block 1204, a feed may be positioned relative to the reflector. Thismay include designing a horn (e.g., 204, FIG. 2) by selecting an initialnumber of flare angles and their initial values, and designing adielectric insert (e.g., 206, FIG. 2) by selecting an initial length L(FIG. 3A) of the portion of the dielectric insert that extends beyondthe aperture of the horn.

At block 1206, an illumination beam directed toward the reflector may besimulated. A cross-polarization of the illumination beam may becomputed. If at block 1208, the cross-polarization is greater than apredetermined value, then processing may proceed to block 1210. At block1210, one or more of the flare angles may be adjusted. Processing mayreturn to block 1206, where a cross-polarization is recomputed with theadjusted flare angle(s). The flare angles may be iteratively adjusted inthis way until the cross-polarization of the illumination beam directedtoward the reflector becomes less than or equal to the predeterminedvalue (goal). At block 1208, when the cross-polarization goal has beenmet, processing may continue to block 1212.

At block 1212, a directivity metric of the illumination beam that isdirected toward the reflector may be computed. If at block 1214, thedirectivity metric is not equal to a predetermined value, thenprocessing may proceed to block 1216. At block 1216, the length L of theportion of the dielectric insert that extends beyond the aperture of thehorn may be adjusted. In some embodiments, the length may be increasedor decrease depending on whether the directivity computed at block 1212is greater than or less than the predetermined value. Processing mayreturn to block 1212, where a directivity metric is recomputed with theadjusted length. The length L may be iteratively adjusted in this wayuntil the directivity metric of the illumination beam directed towardthe reflector reaches the predetermined value (goal), at which time thedesign process may complete.

Referring back to block 1204, in some embodiments, a feed array (e.g.,1000, FIG. 10) may be positioned relative to the reflector. At block1206, the cross-polarization may be computed for an illumination beam ofat least one of the feeds in the feed array directed towards thereflector. At block 1208, the flare angles of each of the feedscomprising the feed array may be adjusted, and the process may beiterated until the cross-polarization of the illumination beam becomesless than or equal to a predetermined value. Similarly, in blocks1212-1216, the lengths of each dielectric insert in the feed array maybe iteratively adjusted until the directivity metric of an illuminationbeam from at least one of the feeds in the feed array reaches apredetermined value.

Referring back to block 1206, in some embodiments, cross-polarizationmay be computed for two or more angles of the illumination beam. Atblock 1208, the cross-polarization goal may be that thecross-polarization for each angle of the illumination beam be less thanor equal to a predetermined value. In some embodiments, each angle mayhave a corresponding predetermined value that the cross-polarization iscompared to.

In other embodiments, at block 1206, cross-polarization may be computedfor two or more frequencies of the illumination beam. At block 1208, thecross-polarization goal may be that the cross-polarization for eachfrequency be less than or equal to a predetermined value. In someembodiments, each frequency may have a corresponding predetermined valuethat the cross-polarization is compared to.

Referring to FIG. 13, an illustrative implementation of a design systemto facilitate the design of a feed (e.g., 202, FIG. 2) may include acomputer system 1302 having a processing unit 1312, a system memory1314, and a system bus 1311. The system bus 1311 may connect varioussystem components including, but not limited to, the processing unit1312, the system memory 1314, an internal data storage device 1316, anda communication interface 1313. In a configuration where the computersystem 1302 is a mobile device (e.g., smartphone, computer tablet), theinternal data storage 1316 may or may not be included.

The processing unit 1312 may comprise a single-processor configuration,or may be a multi-processor architecture. The system memory 1314 mayinclude read-only memory (ROM) and random access memory (RAM). Theinternal data storage device 1316 may be an internal hard disk drive(HDD), a magnetic floppy disk drive (FDD, e.g., to read from or write toa removable diskette), an optical disk drive (e.g., for reading a CD-ROMdisk, or to read from or write to other high capacity optical media suchas the DVD, and so on). In a configuration where the computer system1302 is a mobile device, the internal data storage 1316 may be a flashdrive.

The internal data storage device 1316 and its associated non-transitorycomputer-readable storage media provide nonvolatile storage of data,data structures, computer-executable instructions, and so forth.Although the description of computer-readable media above refers to aHDD, a removable magnetic diskette, and a removable optical media suchas a CD or DVD, it is noted that other types of media which are readableby a computer, such as zip drives, magnetic cassettes, flash memorycards, cartridges, and the like, may also be used, and further, that anysuch media may contain computer-executable instructions for performingthe methods disclosed herein.

The system memory 1314 and/or the internal data storage device 1316 maystore a number of program modules, including an operating system 1332,one or more application programs 1334, program data 1336, and otherprogram/system modules 1338. For example, the application programs 1334,which when executed, may cause the computer system 1302 to performmethod steps of FIG. 12. The application programs 1334 may also includesimulation software (e.g., the HFSS software mentioned above). Anexternal data storage device 1342 may be connected to the computersystem 1302, for example, to store the design data for a feed or feedarray.

Access to the computer system 1302 may be provided by a suitable inputdevice 1344 (e.g., keyboard, mouse, touch pad, etc.) and a suitableoutput device 1346, (e.g., display screen). In a configuration where thecomputer system 1302 is a mobile device, input and output may beprovided by a touch sensitive display.

The computer system 1302 may operate in a networked environment usinglogical connections via wired and/or wireless communications to one ormore remote computers (not shown) over a communication network 1352. Thecommunication network 1352 may be a local area network (LAN) and/orlarger networks, such as a wide area network (WAN).

Embodiments described herein can provide a very light weight solutionfor enhanced aperture directivity to achieve a near optimum efficiencythat improves off-axis cross-polarization that is applicable to highthrough-put satellite antenna architectures. The light weight attributecan be increasingly important for arrays of feeds of large numbers. Theshaped horn affords optimizing gain, cross-polarization and impedancematch in a feed array environment or for isolated feeds.

The above description illustrates various embodiments of the presentdisclosure along with examples of how aspects of the particularembodiments may be implemented. The above examples should not be deemedto be the only embodiments, and are presented to illustrate theflexibility and advantages of the particular embodiments as defined bythe following claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentsmay be employed without departing from the scope of the presentdisclosure as defined by the claims.

What is claimed is:
 1. An antenna comprising: a horn and a dielectricinsert within the horn, wherein the dielectric insert extends beyond anaperture of the horn; a polarizer coupled to the horn, the polarizercomprising a septum polarizer defining a first waveguide portionassociated with a first polarization and further defining a secondwaveguide portion associated with a second polarization; and a diplexercomprising a first pair of waveguides coupled between the firstwaveguide portion and a first pair of ports associated with the firstpolarization, and further comprising a second pair of waveguides coupledbetween the second waveguide portion and a second pair of portsassociated with the second polarization, wherein each waveguide of thefirst and second pairs of waveguides comprises a filter having awaveguide wall that is shared with another filter of at least one otherwaveguide of the first and second pairs of waveguides.
 2. The antenna ofclaim 1, wherein a first waveguide of the first pair of waveguides and afirst waveguide of the second pair of waveguides are associated with afirst frequency band, and a second waveguide of the first pair ofwaveguides and a second waveguide of the second pair of waveguides areassociated with a second frequency band that is lower than the firstfrequency band.
 3. The antenna of claim 2, wherein the filter of thesecond waveguide of the first pair of waveguides has a waveguide wallthat is shared with the filter of the second waveguide of the secondpair of waveguides.
 4. The antenna of claim 3, wherein the filter of thefirst waveguide of the first pair of waveguides has a waveguide wallthat is shared with the filter of the second waveguide of the first pairof waveguides, and the filter of the second waveguide of the first pairof waveguides has a waveguide wall that is shared with the filter of thesecond waveguide of the second pair of waveguides.
 5. The antenna ofclaim 4, wherein the first and second waveguides are arranged in a row.6. The antenna of claim 5, wherein the row is along an E-plane of thefirst and second pairs of waveguides.
 7. The antenna of claim 5, whereinthe second waveguides of the first and second pairs of waveguides sharea waveguide wall and are between the first waveguide of the first pairof waveguides and the first waveguide of the second pair of waveguides.8. The antenna of claim 4, wherein the first pair of waveguides arearranged in a first row, and the second pair of waveguides are arrangedin a second row.
 9. The antenna of claim 1, further comprising acoupling flange containing the first and second pairs of ports.
 10. Theantenna of claim 1, wherein the dielectric insert is a dielectric tube.11. The antenna of claim 10, wherein the dielectric tube is attached toan interior surface of the horn at a location, and the dielectric tubehas an inner diameter that decreases with distance from the location.12. The antenna of claim 1, further comprising a reflector, wherein thehorn is arranged to illuminate the reflector.
 13. The antenna of claim12, wherein the horn, dielectric insert, polarizer and diplexercorrespond to a first feed of a plurality of feeds arranged toilluminate the reflector.
 14. The antenna of claim 1, wherein the filterof each of the second waveguides of the first and second pairs ofwaveguides has a plurality of E-plane elements.
 15. The antenna of claim14, wherein at least some of the plurality of E-plane elements havevarying stub lengths.
 16. The antenna of claim 14, wherein the filter ofeach of the second waveguides of the first and second pairs ofwaveguides includes at least one of an input-matching section and anoutput-matching section.
 17. The antenna of claim 1, wherein the filterof each of the first waveguides of the first and second pairs ofwaveguides has at least one of an H-plane iris or an E-plane element.18. The antenna of claim 1, where the filter of the first waveguide ofthe first pair of waveguides is the same as the filter of the firstwaveguide of the second pair of waveguides, and the filter of the secondwaveguide of the first pair of waveguides is the same as the filter ofthe second waveguide of the second pair of waveguides.
 19. The antennaof claim 1, wherein the filter of the first waveguide of the first pairof waveguides and the filter of the first waveguide of the first pair ofwaveguides are on opposing sides of a dividing plane, and the filter ofthe first waveguide of the second pair of waveguides and the filter ofthe first waveguide of the second pair of waveguides are on opposingsides of a dividing plane.
 20. The antenna of claim 1, whereindirectivity of the horn and dielectric insert is greater thandirectivity due to the aperture of the horn.